Minimalist Li-Ion Charger

Independently charge 10 Li-Ion cells @ 1A each, with $18 of Prime parts and an ATX supply.

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To get an accurate capacity reading from scavenged Li-Ion cells, you will likely need to charge/discharge them at least twice.
The charging of the cells proved to be a bottleneck.
This build made that task about 10x faster than my desktop charger, and for less money.

My desktop Li-Ion charger took 4-6 hours to fully charge 2 cells.   2@500mAh

My discharger took a little over 2 hours to fully discharge 4 cells.

After I discovered I needed to cycle each cell again to get an accurate reading, I was waiting on the charging cycle for most of the time.

This build combines some cheap Amazon USB charger modules based on the TP4056 chip which are less than a buck each, some decent (but cheap) Amazon cell holders, some polycarbonate for a housing, and a hacked up ATX supply to do the same task 10x faster.  Here is a link to the parts I used.  Those modules also contain simple output protection for driving a circuit, which I don't use here, but they were the same cost as the ones without it.

I limited the stock ATX supply airflow and drilled a couple well placed holes in my housing.  This let me use the airflow from the ATX supply to cool the cells and charger modules.  The modules still get warm (as they are linear components delivering 1A each), but the cells now stay nice and cool during charging.  

The ATX supply itself I got from a metal scrap yard for about $1.50.  I bought three, two worked.  It is running here at <20% rated output and could probably run with zero airflow.  In any case, it stays cool as well.

The charger modules are designed to be directly connected to a cell, and so have no reverse polarity protection.  Plug in a cell backwards, and at the very least you'll be buying a new one.  Minimalistic comes with responsibility.  :)  Enjoy.

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hesam.moshiri wrote 02/21/2019 at 08:48 point

The ATX grounds should be isolated, otherwise there would be short circuits between batteries. is it so? I'm not quite sure

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Daren Schwenke wrote 02/27/2019 at 07:43 point

If you were trying to make an actual BMS out of this, yes.. all of them would need to be electrically isolated to charge them while in series.  As it stands, I believe all the modules share the + leg directly.  Not sure, but it is definitely not isolated as this is a linear component and no inductors to be found.

However, that was not the intent here.  This was designed to be a charger which charges single cells (but 10 at a time), for the purpose of topping them off so I can discharge them and get a good reading.  That is all.

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Simon Merrett wrote 02/20/2019 at 08:16 point

Hi Daren, Brian Benchoff noted the lack of reverse polarity protection in his blog write-up. How about some P-FETs and resistors to handle that? I hate to think of the consequences of an absent minded insertion (although I haven't actually looked into what they would be). 

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Daren Schwenke wrote 02/20/2019 at 08:24 point

Since the cells are all individual, the results would probably just be be one less working charging module.  There is an output N-fet of small size onboard.  Either that or the charger module itself is going to pop.  I'm guessing the onboard traces could handle about 5A before turning to vapor as well, so I think the effect will be self limiting in the worst case.

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Simon Merrett wrote 02/20/2019 at 08:45 point

Has had a decent go at exploring the options. I like his idea of a buzzer to tell you that a cell is the wrong way around. Once you install protection it's hard to tell you have put it in wrong (apart from charging led colour) and coming back hours later to find a still-empty cell is probably so annoying that it makes the protection circuit worthwhile! 

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ActualDragon wrote 02/12/2019 at 15:25 point

you can also get these:, and just leave the top off, i made a little 3s li-ion battery out of one, they're awesome little powerbanks

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Daren Schwenke wrote 02/12/2019 at 19:07 point

I was trying to avoid charging the cells in parallel so a bad one can't pull down the entire cycle.  This charges each cell individually for that reason.  Used cells of unknown quality and all.  

I've had a couple cells that just sit there turning charge into heat, and never dropping below the cutoff threshold.  The charger has no idea if you have 1 or 20 cells in parallel so it just keeps delivering power.  Some got scary hot in the process, hence the active cooling now.  I'm doubling the heating now if I put a bad cell in, but at least it will fail all by itself.

That being said, your solution would make a good charger for lots of 'good' cells.  :)

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Mike Szczys wrote 02/11/2019 at 23:31 point

Geez, you're getting a million great projects out of these cells. I loved the capacity tester ( #Minimalist Li-Ion Discharger/Capacity meter. ) and of course the spot welder ( #Minimalist Li-Ion Cell Welder ) is delicious -- can't believe it's that simple.

Great job all around.

Once you get that mountain board battery pulled together, how long do you think it will last? I longevity of salvaged cells just a matter of wise maintenance?

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Daren Schwenke wrote 02/12/2019 at 02:31 point

That is the one area I have thus far spent money, to save money. It has a proper BMS just because my son will be the one managing it, and I imagine running it completely dead would happen on the first run otherwise.  It was like $20 on Amazon.  I don't know how long the cells will last as they are all used, but I am within the proper rate of discharge with my 5p pack, so it should be a decent amount of time.  I'll be happy if I get a year out of them.  Given I probably saved $300 on the battery alone, I'll take what I can get.  I can always build another one now.  :)

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